The present invention relates to a defect inspection method and defect inspection apparatus used to inspect and observe defects, foreign particle, and the like, on the micro-patterns formed on a substrate through a thin-film forming process represented by manufacturing processes for semiconductors or flat-panel displays.
Fine structuring of the patterns formed with photolithography is progressing with the enhancement of semiconductor integration density and the improvement of flat-panel display resolution. During the manufacturing processes for these products, after the patterns have been formed, they are subjected to defect inspection and/or the like in order to improve production yields. During the defect inspection, the patterns are detected as images by optical system etc., then these images are compared with those of adjacent dies (or cells), and defects are extracted on the basis of comparison results.
Incidentally, the resolution-improving technology disclosed in Japanese Patent Application Laid-Open Publication No. 2000-155099 (corresponding to U.S. application Ser. No. 09/397,334) is known as an ultrahigh-resolution detection technology that uses wavelength reduction and light polarization with conventional defect inspection optical system.
In the above ultrahigh-resolution detection technology that uses light polarization, specific polarized light is irradiated onto a sample via a dry-system objective lens by incident illumination, the light thus reflected/diffracted is captured by the same objective lens, and an image of the sample is detected using an image sensor. The conventional technology has had the characteristic that an optical image of the sample can be obtained with high contrast by detecting this image using only specific polarized components of the reflected/diffracted light.
In the generation of hyperfine-structuring into pattern sizes of sub-100 nm, however, pattern images have been becoming difficult to accurately detect, since sufficient resolution has not been made obtainable using only the resolution-improved defect inspection optical system mentioned above. The need is therefore arising to improve resolution by using defect inspection optical system enhanced further in numerical aperture (NA).
Additionally, in a sample, represented by a semiconductor wafer, that has undergone a thin-film forming process as the object to be inspected, a transparent film made of silicon dioxide (SiO2), for example, is formed as an interlayer-insulating film. This insulating film has thickness unevenness in the wafer. During the inspection, such film thickness unevenness should originally not be detected since it has no fatal influence with respect to device characteristics. During observation through a dry-system lens, however, thin-film interference on the transparent film causes the unevenness of the film thickness to appear as the unevenness of brightness on the image detected. For example, during comparative inspection with respect to adjacent dies, if the transparent films on these adjacent dies are uneven in film thickness, differences in the brightness of the respective images detected will occur and an image of the object will be incorrect-detected as a defect image. Increasing an inspection threshold value in an attempt to avoid such incorrect-detection will pose the problem that total inspection sensitivity decreases.
In addition, since their pattern materials and surface irregularities will differ according to the manufacturing processes and product types, the objects to be subjected to defect inspection will be of various types and forms.